Oops. Lathe workholding issues.

[Suzuki4evr]

Set it up in the lathe, and hit it with some Locktite Superglue, or some of the girlfriends ( or your own) fingernail polish. Acetone/heat will release when done.

and darkzero, I'll have your baby, you clever thang you. Brilliant.

 

[Mauser lover]

...make your own hex mandrel to drive the screw.

Sounds good. How? I don't have a dividing head at the moment for my mill. Any other way? If not, I might just have to be happy with it.

There is a little bit of a center mark in the head of the screw. If there is a way to hold it between centers, and still drive it somehow, I think that would be ideal. Ideas on that one?

 

[ThinWoodsman]

Sounds good. How? I don't have a dividing head at the moment for my mill. Any other way? If not, I might just have to be happy with it.

Hex collet block.

But really you can just buy some hex rod, and shave it down as needed to tightly fit the socket cap screw. The more important bit is the concentricity you'll get turning part of the hex rod down to a round shaft in the lathe.

 

[Tozguy]

Sometimes a Torx bit will fit the hex head tighter than a hex wrench does.

 

[darkzero]

Sounds good. How? I don't have a dividing head at the moment for my mill. Any other way? If not, I might just have to be happy with it.

Collet block would be the quickest but if you don't have any type of indexing device it can still be done easily a number of ways. Here's a few methods off the top of my head.

Piece of round stock, drill & tap one end for a hex head bolt, diameter of head smaller than the round stock. Heck you could even just drill & glue the bolt in, as long as it's secure. Clamp the round stock in the vise using the hex bolt to index. Eyeball & line up one flat of the hex head with the top surface of the vise. Make the cut, rotate & repeat. You could even remove the endmill after each cut, put a piece of round stock in the spindle with the end faced flat & use that to touch off on the next flat of the hex head. Of course you could even indicate it in but I would just eyeball, much quicker & it doesn't need to be precise.

Or don't even need to use a hex bolt to index. Cut the flat, rotate, use a protractor touching the flat & say the table surface to cut the next flat.

Get a bigger hex head bolt & with enough length, use a piece of stock to support the shaft of the bolt, clamp the head in the vise with 2 V-blocks, cut the flat, rotate & repeat. if you don't have v blocks you can quickly make some by just making a cut with an endmill at 45°.

 

[Mauser lover]

Hex collet block.

But really you can just buy some hex rod, and shave it down as needed to tightly fit the socket cap screw. The more important bit is the concentricity you'll get turning part of the hex rod down to a round shaft in the lathe.

Ah! I think we've got a winner here! I don't have a collet block (yet. Budgets are inconvenient, aren't they!), and my mill is probably less precise than the screw I've already got anyway! It's a well-loved Rong-Fu round column benchtop machine. Will probably upgrade sometime in the distant future, but a surface grinder is on my list before a Bridgeport. And a concrete shop is on my list before that! Anyway, back to the idea at hand!

I'm puzzled by what you mean by "The more important bit is the concentricity you'll get turning part of the hex rod down to a round shaft in the lathe."

Are you saying that I buy 3/16 hex stock (the size I need for driving my screw) and turn part of it down, put the round part in my chuck while noting which side is "up" so the runout cancels itself out?

I'm also contemplating getting 3/16 hex stock and machining a steep taper on the very end of it so it contacts the head of the screw in the shallow taper inside the socket while also providing enough contact with the socket to drive the screw.

Just to be clear and restating my goals...
I'm center drilling the threaded end of the screw while holding the threads in the chuck. I move the screw out of the chuck to be driven by a hex tool bit (either something I make, or something made across the sea) and held by a live center and finishing the machining there. I'm taking material off the diameter of the head as well as the shank, and my goal is to have everything be concentric with the socket in the head and the center drilled shank.
Did I miss anything? I did mention that I am a beginner, right? In case you couldn't tell.

Also, I did try the Torx bit. It is just a hair tighter. It is about .002 bigger across the flats than the hex bit. If all else fails, I might go for that, but it is still too wobbly for my tastes.

 

[brino]

Is there a metric hex driver bit that works out to fit a little tighter?
-brino

 

[Mauser lover]

Nope, tried the metrics already. Goes from spinning freely inside the socket to not fitting.

 

[ThinWoodsman]

I'm puzzled by what you mean by "The more important bit is the concentricity you'll get turning part of the hex rod down to a round shaft in the lathe."

Are you saying that I buy 3/16 hex stock (the size I need for driving my screw) and turn part of it down, put the round part in my chuck while noting which side is "up" so the runout cancels itself out?

That is pretty much what I was suggesting. Put the hex rod in the chuck, get it to run true (basically do something clever with a plunger dial indicator to verify that all six sides are at the same measurement - a bit tricky to know when each face is true to the previous, but you can prob use a machinist's square on the lathe bed to square up each face), then turn down to a cylinder. Hold the cylinder in the chuck. That should make it easier to re-chuck the thing. I might be over-simplifying here and it may be better to just use the hex rod without turning it. If the rod isn't centered when you turn it, the end result will be worse than just using the hex shape.

And of course you will probably need to skim the flats of the hex with the mill, which probably should be done before chucking the thing, just make sure the newly-milled end is inside the chuck a bit so the jaws don't mar it.

Sounds like you pretty much have the idea. What you described in your restating-of-goals should work.

 

[Mark Needham]

Did you try Superglue, nail polish, or locktite, shoot even wood glue, PVA, shellac, dopping wax even bondo. Spit on the mother.
Nail polish, et al, would even allow you time to attain your concentricity.
Just need to know if you have tried it yet?